Moon, Jupiter and Bright Star Show Off in Night Sky This Week

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Check out the east-northeast sky after about 11 p.m. local time
late Thursday and Friday evening (Oct. 4 and 5) for
a changing celestial array involving the moon, a bright
planet and a bright star, weather permitting.

The planet in question is
Jupiter, usually the second brightest planet next to
Venus. At a dazzling magnitude of -2.6 on the astronomers'
brightness scale (the lower the number, the brighter the object),
Jupiter shines three times brighter than Sirius, the brightest
star. Whenever it's above the horizon, Jupiter, the solar
system's biggest planet at 88,800 miles (143,000
kilometers) in diameter — always attracts immediate
attention; to the eye it resembles a brilliant silvery white,
non-twinkling "star."

Currently, Jupiter is 419 million miles (674 million km) from
Earth. Although primarily an after-midnight sight right now,
Jupiter is rising an average of just over 4 minutes earlier each
night. By Dec. 3 it will arrive at opposition and be
visible all night from sunrise to sunset.

One star in the V stands out far more than the others. That's
Aldebaran, marking the Bull's angry orange-red
eye. This star seems like it's a member of the Hyades, but
in reality, it's only an innocent bystander; it's lined up
almost perfectly with the other neighboring stars to fill out the
V-shaped pattern, but it's actually much closer to the Earth at a
distance of 65 light-years, compared to the Hyades, which is more
than double that distance at 153 light-years away.

The moon is currently on the wane, with full phase having
occurred this past weekend; last quarter (or half
phase) will come early on Monday (Oct. 8). So a gibbous moon
will be interacting with Jupiter and Aldebaran late
this Thursday and Friday nights.

Late Thursday night, the moon will form a right
triangle with Aldebaran and Jupiter. The moon will stand about 5
degrees above Aldebaran, which in turn sits about 7 degrees to
the right of Jupiter. Your clenched fist held at arm's
length measures roughly 10 degrees.

Late on Friday night, the moon will have shifted noticeably past
Jupiter, and will stand about 5 degrees to Jupiter's lower left —
while at the same time the moon will be about 10 degrees ("one
fist") to the left of Aldebaran.

In addition to our own moon, there are four other moons that you
might want to look at, namely the famous Galilean Satellites,
which were first seen by Galileo with his crude telescope in
1610.

These satellites of Jupiter are fun to watch as they change their
position relative to their host planet from hour to hour and
night to night. They can be glimpsed through 7-power
binoculars (if you hold them steady) or better yet, a
small telescope.

On both Thursday and Friday nights you can see all four moons —
two on either side of Jupiter. On Thursday night, on one
side, you'll see Europa and Ganymede, while on the side, spaced
farther apart are Io and Callisto. On Friday night, Ganymede
and Io will be relatively close to each other, while on the other
side near to Jupiter will be Europa, with Callisto farther out
from "Big Jupe."

Joe Rao serves as an instructor and guest lecturer at New
York's Hayden Planetarium. He writes about astronomy for The New
York Times and other publications, and he is also an on-camera
meteorologist for News 12 Westchester, New York.